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APPENDIX D: RESISTANCE WELDING BASICS
identical materials with thickness ratios greater than 4 to 1. The general rule is that the
more resistive material or the thinner material should be placed against the negative (-)
electrode.
Weld Strength Testing
Destructive tests should be performed on a random basis using actual manufacturing parts.
Destructive tests made on spot welds include tension, tension-shear, peel, impact, twist,
hardness, and macro-etch tests. Fatigue tests and radiography may also be used. Of these
methods, torsional shear is preferred for round wire and a 45 degree peel test for sheet stock.
Weld Strength Profiles
Creating a Weld Strength Profile offers you a scientific approach to determining the optimum set
of welding parameters and then displaying these parameters in a graphical form.
1.
Start at a low weld current, make five or more welds, then perform pull tests for each
weld. Calculate the average pull strength. Increase weld current and repeat this
procedure. Do not change the weld time, weld force, or electrode area.
2.
Continue increasing weld current until any unfavorable characteristic occurs, such as
sticking or spitting.
3.
Repeat steps 1 and 2 for different weld forces and then create a plot of part pull strength
versus weld current for different weld forces as shown in Figure D-2.
4.
Repeat steps 1 through 3 using a different, but fixed weld time.
Weld Strength Profile
IP-215A/IP-217A FINE SPOT WELDING POWER SUPPLIES
D-8
993-603 REV A: October, 1996
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